When you think of a family tree, you probably think of human ancestry, and how we can trace our ancestors back to different geographical regions. All living things have a common family tree, which can be seen in our genetic code. While stars aren’t living things, they have a similar family tree, and we’re starting to gather enough data to piece it together.
We’ve long known that stars can be categorized into generations depending on their origin. The very first generation of stars formed from the hydrogen and helium formed in the big bang. When the largest of those stars died in supernovae, the remnant gas and dust collapsed to form a new generation of stars. The largest second-generation stars later exploded, a third generation of stars formed, and so on. Since heavier elements such as carbon and iron forms within stars, later generations of stars tend to have a higher metallicity. Our Sun, for example, has a relatively high metallicity, and is therefore a third or fourth generation star.
As our observations of stars has increased, there have been efforts to find stellar siblings of our Sun. Stars don’t form on their own, but rather form with other stars in large nebulae known as stellar nurseries. Stars formed in the same stellar nursery would have similar ages and similar chemical compositions. The more similar the composition and age, the more likely the stars are to be related.
With sky survey satellites such as Gaia, we are finally gathering this kind of information on millions of stars, so in principle we should be able to study the connections between stars and groups of stars. A new paper in MNRAS shows how this can be done. By piecing together a stellar family tree, we can better understand the dynamics of stellar evolution within our galaxy.
Paper: Paula Jofré et al. Cosmic phylogeny: reconstructing the chemical history of the solar neighbourhood with an evolutionary tree. MNRAS 467 (1): 1140-1153. (2017)